Application of potassium, zinc and boron as potential plant growth modulators in Gossypium hirsutum L. under heat stress

High temperature stress at reproductive stages of cotton crop severely affects the yield and quality of cotton crop under changing climatic conditions. To alleviate the adverse effects of high temperature stress on cotton crop, the regulatory effects of potassium (K), zinc (Zn), and boron (B) were assessed by applying different temperature regimes at three reproductive stages of cotton crop under field and glass house conditions. Cotton plants were subjected to low (32/20 °C ± 2), medium (38/24 °C ± 2), and high (45/30 °C ± 2) temperatures under glasshouse, but sown at specific dates in field to provide different temperatures at three reproductive stages. High-temperature stress at squaring, flowering and boll formation stages in both field studies increased relative cell injury (RCI), total soluble proteins (TSP), reactive oxygen species and reduced fiber yield attributes i.e. total number of bolls per plant (TNBPP), number of sympodial branches per plant (NSBPP) and quality traits. For example, RCI, TNBPP and fiber fineness were reduced by 73%, 42% and 29%, respectively under supra thermal regime (SupTR) of glass house study over the optimal thermal regime (OpTR). Foliar application of K and Zn followed by B increased TSP, RWC, TNBPP, NSBPP, fiber fineness, fiber length and fiber strength. Further, foliar spray of K and Zn followed by B also reduced H2 O2 under SupTR and SubTR over the OpTR. The findings of the present study clearly demonstrate that foliar spray of Zn, K and B alleviated adverse effects of high temperature stress at squaring, flowering and boll formation stages and increased seed cotton yield and quality of cotton crop. © TÜBİTAK

Association of jasmonic acid priming with multiple defense mechanisms in wheat plants under high salt stress

Salinity is a global conundrum that negatively affects various biometrics of agricultural crops. Jasmonic acid (JA) is a phytohormone that reinforces multilayered defense strategies against abiotic stress, including salinity. This study investigated the effect of JA (60 μM) on two wheat cultivars, namely ZM9 and YM25, exposed to NaCl (14.50 dSm−1) during two consecutive growing seasons. Morphologically, plants primed with JA enhanced the vegetative growth and yield components. The improvement of growth by JA priming is associated with increased photosynthetic pigments, stomatal conductance, intercellular CO2, maximal photosystem II efficiency, and transpiration rate of the stressed plants. Furthermore, wheat cultivars primed with JA showed a reduction in the swelling of the chloroplast, recovery of the disintegrated thylakoids grana, and increased plastoglobuli numbers compared to saline-treated plants. JA prevented dehydration of leaves by increasing relative water content and water use efficiency via reducing water and osmotic potential using proline as an osmoticum. There was a reduction in sodium (Na+) and increased potassium (K+) contents, indicating a significant role of JA priming in ionic homeostasis, which was associated with induction of the transporters, viz., SOS1, NHX2, and HVP1. Exogenously applied JA mitigated the inhibitory effect of salt stress in plants by increasing the endogenous levels of cytokinins and indole acetic acid, and reducing the abscisic acid (ABA) contents. In addition, the oxidative stress caused by increasing hydrogen peroxide in salt-stressed plants was restrained by JA, which was associated with increased α-tocopherol, phenolics, and flavonoids levels and triggered the activities of superoxide dismutase and ascorbate peroxidase activity. This increase in phenolics and flavonoids could be explained by the induction of phenylalanine ammonia-lyase activity. The results suggest that JA plays a key role at the morphological, biochemical, and genetic levels of stressed and non-stressed wheat plants which is reflected in yield attributes. Hierarchical cluster analysis and principal component analyses showed that salt sensitivity was associated with the increments of Na+, hydrogen peroxide, and ABA contents. The regulatory role of JA under salinity stress was interlinked with increased JA level which consequentially improved ion transporting, osmoregulation, and antioxidant defense

Comparative transcriptome analysis of respiration-related genes in nodules of phosphate-deficient soybean (Glycine max cv. Williams 82)

A transcriptome analysis was used to compare the nodule transcriptomes of the model soybean ‘Williams 82’ inoculated with two Bradyrhizobium diazoefficiens strains (USDA110 vs. CB1809) under phosphate (Pi) deficiency. The entire dataset revealed a core set of low-Pi-responsive genes and recognized enormous differential transcriptional changes between the Pi-deprived USDA110-nodules and CB1809-nodules. The lower symbiotic efficiency of the Pi-starved USDA110 nodules was ascribed to the downregulation of an F1-ATPase gene engaged in oxidative phosphorylation, more likely contributing to diminished ATP production. To cope with energy shortage caused by Pi stress, the Pi-deprived USDA110-nodules preferentially upregulated the expression of a large number of genes encoding enzymes implicated in specialized energy-demanding pathways, such as the mitochondrial respiratory chain (i.e., cytochrome c oxidase), alcoholic fermentation (i.e., pyruvate decarboxylase and alcohol dehydrogenase) and glycolysis (e.g., hexokinase, phosphofructokinase, glyceraldehyde‐3‐phosphate dehydrogenase and pyruvate kinase). These respiratory adjustments were likely associated with higher metabolic cost and redox imbalance, thereby, negatively affecting nodule symbiosis under Pi deprivation. In contrast, the Pi-starved CB1809-nodules reduced the metabolic cost by regulating a lower number of genes and increasing the expression of genes encoding proteins implicated in non-phosphorylating bypasses (e.g., flavoprotein alpha and flavoprotein:ubiqionone oxidoreductase), which could promote the carbohydrate utilization efficiency and energy metabolism. Notably, the upregulation of a transcript encoding a malate dehydrogenase could boost the CB1809-nodules under Pi stress. The dynamic shifts in energy metabolism in the Pi-deprived USDA110-nodules and CB1809-nodules could be transformative to upgrade the mechanistic/conceptual understandings of soybean adaptation to Pi deficiency at the transcriptional level

Trichoderma: The “secrets” of a multitalented biocontrol agent

The plant-Trichoderma-pathogen triangle is a complicated web of numerous processes. Trichoderma spp. are avirulent opportunistic plant symbionts. In addition to being successful plant symbiotic organisms, Trichoderma spp. also behave as a low cost, effective and ecofriendly biocontrol agent. They can set themselves up in various patho-systems, have minimal impact on the soil equilibrium and do not impair useful organisms that contribute to the control of pathogens. This symbiotic association in plants leads to the acquisition of plant resistance to pathogens, improves developmental processes and yields and promotes absorption of nutrient and fertilizer use efficiency. Among other biocontrol mechanisms, antibiosis, competition and mycoparasitism are among the main features through which microorganisms, including Thrichoderma, react to the presence of other competitive pathogenic organisms, thereby preventing or obstructing their development. Stimulation of every process involves the biosynthesis of targeted metabolites like plant growth regulators, enzymes, siderophores, antibiotics, etc. This review summarizes the biological control activity exerted by Trichoderma spp. and sheds light on the recent progress in pinpointing the ecological significance of Trichoderma at the biochemical and molecular level in the rhizosphere as well as the benefits of symbiosis to the plant host in terms of physiological and biochemical mechanisms. From an applicative point of view, the evidence provided herein strongly supports the possibility to use Trichoderma as a safe, ecofriendly and effective biocontrol agent for different crop species

The Integration of Bio and Organic Fertilizers Improve Plant Growth, Grain Yield, Quality and Metabolism of Hybrid Maize (Zea mays L.)

Expanding eco-friendly approaches to improve plant growth and crop productivity is of great important for sustainable agriculture. Therefore, a field experiment was carried out at the Faculty of Agriculture Farm, Mansoura University, Egypt during the 2018 and 2019 growing seasons to study the effects of different bio- and organic fertilizers and their combination on hybrid maize growth, yield, and grain quality. Seeds were treated with Azotobacter chrocoocum, arbuscular mycorrhizal fungi (AMF), Bacillus circulans, biogas slurry, humic acid (HA), and their combination aiming to increase the growth and yield of maize and to reduce the need for chemical fertilizers. The results showed that combined application of the biofertilizer mixture (Azotobacter chrocoocum, AMF, and Bacillus circulans) with organic fertilizers enhanced maize growth, yield, and nutrient uptake. Moreover, the bio-organic fertilization has improved the soluble sugars, starch, carbohydrates, protein, and amino acid contents in maize seeds. Additionally, the bio-organic fertilization caused an obvious increase in the microbial activity by enhancing acid phosphatase and dehydrogenase enzymes, bacterial count, and mycorrhizal colonization levels in maize rhizosphere as compared with the chemical fertilization. Additionally, the bio-organic fertilizers has improved α-amylase and gibberellins (GA) activities and their transcript levels, as well as decreased the abscisic acid (ABA) level in the seeds as compared to the chemical fertilizers. The obtained results of bio-organic fertilization on the growth parameters and yield of maize recommend their use as an alternative tool to reduce chemical fertilizers

Arbuscular mycorrhizae mitigate aluminum toxicity and regulate proline metabolism in plants grown in acidic soil

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and induce stress tolerance. Proline is reported to accumulate in mycorrhizal plants under stressful conditions, such as aluminum (Al) stress. However, the detailed changes induced in proline metabolism under AMF–plant symbiosis has not been studied. Accordingly, this work aimed to study how Al-stressed grass (barley) and legume (lotus) species respond to AMF inoculation at growth and biochemical levels. The associated changes in Al uptake and accumulation, the rate of photosynthesis, and the key enzymes and metabolites involved in proline biosynthesis and degradation pathways were studied. Soil contamination with Al induced Al accumulation in tissues of both species and, consequently, reduced plant growth and the rate of photosynthesis, while more tolerance was noticed in lotus. Inoculation with AMF significantly reduced Al accumulation and mitigated the negative impacts of Al on growth and photosynthesis in both species; however, these positive effects were more pronounced in barley plants. The mitigating action of AMF was associated with upregulation of proline biosynthesis through glutamate and ornithine pathways, more in lotus than in barley, and repression of its catabolism. The increased proline level in lotus was consistent with improved N metabolism (N level and nitrate reductase). Overall, this study suggests the role of AMF in mitigating Al stress, where regulation of proline metabolism is a worthy mechanism underlying this mitigating action

Effect of Irrigation Regimes and Soil Texture on the Potassium Utilization Efficiency of Rice

Understanding the effects of irrigation regime and soil texture on potassium-use efficiency (KUE) of rice (Oryza sativa. L) is essential for improving rice productivity. In this regard, experiments were conducted from July to October in 2016 and 2017 by using a randomized complete block design in a factorial arrangement with four replications. The rice plants were grown in three soils, with clay contents of 40%, 50%, and 60%, which were marked as S (40%), S (50%), and S (60%), respectively. For each soil type, irrigation regimes, namely, R (F, S100%), R (F, S90%), and R (F, S70%), were established by setting the lower limit of irrigation to 100%, 90%, and 70% of saturated soil water content, respectively, and the upper limit of irrigation with 30 mm of flooding water above the soil surface for all irrigation regimes. Results showed that the responses of the roots and shoots and the potassium accumulation (KA) and KUE of rice were significantly affected by the water regime and soil texture. In the same irrigation regime, increasing the soil clay content improved the K utilization of rice. Under the same soil type, R (F, S100%) was the optimal water management practice for growing rice. The R (F, S100%) S (60%) treatment presented the highest KUE, which was 56.4% in 2016 and 68.1% in 2017. The R (F, S70%) S (40%) treatment showed the lowest KUE, which was 13.8% in 2016 and 14.9% in 2017. These results enrich knowledge regarding the relationship among soil, water, and rice, and provide valuable insights on the effect of irrigation regime and soil texture on the KA and KUE of rice